Subject: [PATCH] Fix control messages are inflated

RFC7692 states that control messages should not be compressed so there is no
need to inflate these messages.

There can be a bug if a control message is received while processing a
compressed message since lws relies on the RSV bit of the first message to
inflate the rx buffer or not.
Here we also check the opcode to only inflate a message if it is a data message.

Fixes: #1470